EP2152760B1 - Nitrile rubbers - Google Patents

Abstract

The present application provides novel nitrile rubbers comprising repeating units of at least one α,β-unsaturated nitrile, at least one conjugated diene and optionally one or more further copolymerizable monomers which nitrile rubbers are distinguished by a specific calcium content as well as a specific chlorine content and dispose of specific thio end groups. Additionally, an improved polymerization and work-up process is provided to produce the aforementioned nitrile rubbers.

Description

The invention relates to a nitrile rubber, a process for its preparation, vulcanizable mixtures based on this nitrile rubber, furthermore a process for the preparation of vulcanizates from these mixtures and the vulcanizates obtained thereby.

Nitrile rubbers, also abbreviated to "NBR", are understood to mean rubbers which are copolymers or terpolymers of at least one α, β-unsaturated nitrile, at least one conjugated diene and optionally one or more further copolymerizable monomers.

The problem is often the storage stability of such nitrile rubbers. In this case, storage stability means that the Mooney viscosity, as an important specification criterion for nitrile rubbers, changes as little as possible during long storage times and in particular also at relatively high temperatures, which can occur in summer.

Nitrile rubbers and processes for making such nitrile rubbers are known, see eg W. Hofmann, Rubber Chem. Technol. 36 (1963) 1 and Ullmann's Encyclopedia of Industrial Chemistry, VCH Verlagsgesellschaft, Weinheim, 1993, pp. 255-261 , There is no indication in these publications as to whether and, if appropriate, how to improve the storage stability of nitrile rubbers.

JP 75,105,746 describes heat-resistant nitrile rubbers obtained by performing latex coagulation with a mixture of tin dichloride and calcium chloride. Per 100 parts by weight of calcium chloride while 50 parts by weight of tin dichloride are used. The use of tin salts is today problematic for environmental reasons, especially since these tin salts can be found in a comprehensive subsequent washing of the nitrile rubber in nitrile rubber. The removal of tin salts from the wash water is associated with a high and therefore-also undesirable cleaning.

Out JP 76 / 26,790 It is known to coagulate a nitrile rubber latex using strontium chloride, resulting in a coagulated nitrile rubber having a strontium content of 1.2%. It is stated that a molded article prepared based on such a nitrile rubber has much better properties than a corresponding nitrile rubber-based molded article obtained from the latex by coagulation with calcium chloride.

According to Angew. Makromol. Chem. 1986, 145-146, 161-179 There is an extremely effective measure to improve the storage stability of nitrile rubber in a selective hydrogenation of the butadiene-derived double bonds while maintaining the triple bonds of the nitrile groups. For many applications, the property changes achieved by the hydrogenation are desired, but not all. The hydrogenation is also complicated and requires a number of additional process steps. In addition, the glass transition temperatures are degraded by the hydrogenation compared to the non-hydrogenated starting material. For this reason, hydrogenation is not a suitable solution to the problem for all applications.

NBR is prepared by emulsion polymerization, initially obtaining an NBR latex. The NBR solid is isolated from this latex by coagulation. For coagulation, salts and acids are used. The coagulation of latices with metal salts is known that monovalent metal ions, for example in the form of sodium chloride, significantly larger amounts of electrolyte are required than polyvalent metal ions, for example in the form of calcium chloride, magnesium chloride or aluminum sulfate ( Colloid-Z. 154, 154 (1957 )). Out Houben-Weyl (1961), Methods of Org. Chemistry, Macromolecular Substances 1, p. 484 it is also known that the use of polyvalent metal ions leads to "a more or less large inclusion of the emulsifier in the product". According to Houben-Weyl (1961), Methoden der Org. Chemie, Macromolecular Substances 1, p. 479 "Not only must the used electrolytes be washed out very carefully, but the finished product should also be free from the catalysts and emulsifiers of the batch." Even small remnants of electrolytes give cloudy and cloudy pressed and injection pieces, spoil the electrical properties and increase the water absorption capacity of the finished product "(quote). In the Houben-Weyl, however, there is no indication as to whether and in what way the work-up of the latex influences its storage stability.

Out DD 154 702 discloses a process for the radical copolymerization of butadiene and acrylonitrile in emulsion, which is controlled by a special, computer-aided dosing program for the monomers and the molecular weight regulator, such as tert-dodecyl mercaptan, and in which the latices obtained by coagulation in an acidic medium for Solid rubber be worked up. As a significant advantage of the method is stated that the resin and / or fatty acid soaps used as emulsifiers remain by the use of acids during coagulation in the rubber, so not washed out as in other methods. For this purpose, in addition to the advantage of good properties of the NBR in particular the improvement of the economy of the process and the avoidance of wastewater pollution by leached emulsifier reclaimed. The butadiene-acrylonitrile copolymers having 10-30 wt.% Of acrylonitrile obtained are said to have good elasticity and low temperature properties combined with increased swelling resistance and processability. Measures by which an influence on the storage stability of the nitrile rubber is possible can not be deduced from the teaching of this patent.

Out JP 27902/73 (Appl. 69 32.322 ) it is known that the use of amines in the coagulation of latices with magnesium salts, for example by combining diethylenetriamine and magnesium chloride, reduces the scorch rate and thus improves the scorch resistance of nitrile rubbers. However, there are no indications as to how storage-stable nitrile rubbers can be obtained.

From the DE-OS 23 32 096 It is known that rubbers can be precipitated from their aqueous dispersions with the aid of methylcellulose and a water-soluble alkali metal, alkaline earth metal, aluminum or zinc salt. The preferred water-soluble salt is sodium chloride. As an advantage of this method is described that a coagulum is obtained which is almost completely free of impurities such as emulsifiers, catalyst residues and the like, since these foreign substances removed together with the water in the separation of the coagulum and any remaining residues completely washed with more water become. Statements on the storage stability of such produced rubbers are not made. In DE-OS 24 25 441 in the electrolytic coagulation of rubber latices as an auxiliary instead of the methylcellulose 0.1-10 wt.% (relative to the rubber) of water-soluble C ₂ -C ₄ alkylcelluloses or hydroxyalkylcelluloses in combination with 0.02 to 10 wt.% (based on the rubber ) of a water-soluble alkali, alkaline earth, aluminum or zinc salt. Again, sodium chloride is used as the preferred water-soluble salt. The coagulum is mechanically separated, optionally washed with water and the remaining water removed. Again, it is stated that the foreign matter as in the DE-OS 23 32 096 when the coagulum is separated, virtually completely removed together with the water, and any remaining residues are washed out completely by washing with further water.

In DE-OS 27 51 786 It is found that the precipitation and isolation of rubbers from their aqueous dispersions can be carried out with a lower amount of (hydroxy) alkylcellulose, when 0.02 to 0.25% by weight of a water-soluble calcium salt is used. It is again described as an advantage that by this method an extremely pure coagulum is obtained, which is virtually completely free from impurities, such as emulsifiers, catalyst residues and the like. These foreign substances are removed together with the water when separating the coagulum and any remaining residues can be washed out with water. It is further stated that the properties of the isolated rubbers are not adversely affected by coagulation with a calcium salt. Rather, one obtains a rubber in which the vulcanization properties are not impaired and fully satisfactory are. This is surprising because degradation of rubber properties is often observed when polymers were precipitated from dispersions using polyvalent metal ions such as calcium or aluminum ions. As evidence of the latter statement will Houben-Weyl (1961), Methods of Org. Chemistry, Macromolecular Substances 1, p. 484/485 used. The rubbers of DE-OS 27 51 786 In contrast, there was no delay or deterioration, for example during scorching and / or vulcanization.

None of the scriptures DE-OS 23 32 096 . DE-OS 24 25 441 and DE-OS 27 51 786 shows what measures must be taken to achieve a high storage stability of nitrile rubbers.

As with the patents described above, it is also the goal of DE-OS 30 43 688 To reduce the amounts of electrolyte required for coagulation of the latex as much as possible. This is done according to the teaching of DE-OS 30 43 688 achieved by using in the electrolytic coagulation of latices in addition to the inorganic coagulant as an aid either on plant-derived proteinaceous materials or polysaccharides such as starch and optionally water-soluble polyamine compounds. As inorganic coagulants, preference is given to describing alkali metal or alkaline earth metal salts. Due to the special additives, it is possible to reduce the quantities of salt necessary for quantitative latex coagulation. Out DE-OS 3,043,688 There is no indication as to how an improvement in the storage stability can be achieved by the preparation and / or work-up of the nitrile rubber.

In the US Patent No. 4,920,176 is described and confirmed by experimental data that coagulation of a nitrile rubber latex with inorganic salts such as sodium chloride or calcium chloride very high sodium, potassium and calcium contents and also emulsifiers remain in the nitrile rubber. However, this is undesirable and in order to obtain a pure as possible Nitrilkautschuks be according to the teaching of US Patent No. 4,920,176 in the coagulation of nitrile rubber latexes instead of the inorganic salts water-soluble cationic polymers used. These are, for example, those based on epichlorohydrin and dimethylamine. These tools aim to significantly reduce the amount of salt remaining in the product. The resulting vulcanizates have a lower swelling in water storage and a higher electrical resistance. In the patent, the mentioned property improvements are purely qualitatively attributed to the minimum cation contents remaining in the product. A further explanation of the observed phenomena is not given. Also will be in US Patent No. 4,920,176 made no statement as to whether and how the storage stability can be controlled by production and processing of the nitrile rubber.

The goal of EP-A-1 369 436 is to provide nitrile rubbers of high purity. The procedure of EP-A-1 369 436 is based on typical nitrile rubbers. Nothing is done about the polymerization process except that an emulsion polymerization is carried out in the presence of fatty acid and / or resin acid salts as emulsifiers. This is followed by latex coagulation with acids, optionally with the addition of precipitants. As acids, it is possible to use all mineral and organic acids which make it possible to set the desired pH values. In addition, additional precipitants can be used, are called for this alkali salts of inorganic acids such as sodium chloride and sodium sulfate. Subsequently, the fatty and resin acids formed by the acid action are washed out with aqueous alkali hydroxide solutions and the polymer is finally subjected to shearing until a residual moisture of less than or equal to 20% is established. In the course of this shearing, the water or the residual moisture, including the ion contents and other foreign substances contained therein, is removed. The Ca contents of the products disclosed in Examples 1 and 2 are only 4 or 2 ppm. The EP-A-1 369 436 provides no indications for the preparation of nitrile rubbers which have an increased storage stability.

In EP-A-0 692 496 . EP-A-0 779 301 and EP-A-0 779 300 Nitrile rubbers based on an unsaturated nitrile and a conjugated diene are described in each case. Common to all nitrile rubbers is that they contain 10-60% by weight of unsaturated nitrile and have a Mooney viscosity in the range of 15-150, or respectively EP-A-0 692 496 of 15-65 and all having at least 0.03 moles of a C ₁₂ -C ₁₆ alkylthio group per 100 moles of monomer units, said alkylthio group including at least three tertiary C atoms and a sulfur atom directly attached to at least one of the tertiary C atoms is bound. The preparation of the nitrile rubbers is carried out in the presence of a correspondingly constructed C ₁₂ -C ₁₆ -alkylthiol as a molecular weight regulator, which acts as a "chain transfer agent" and is thus incorporated as an end group in the polymer chains.

For the nitrile rubbers according to EP-A-0 779 300 It is stated that they have a width "ΔAN" (AN = unsaturated nitrile) of the composition distribution of the unsaturated nitrile in the copolymer in the range of 3 to 20. The process for their preparation differs from that of EP-A-0 692 496 in that only 30-80% by weight of the total amount of monomer is used at the beginning of the polymerization and the remaining amount of monomer is metered in only at a conversion of the polymerization of 20-70% by weight.

For the nitrile rubbers according to EP-A-0 779 301 is stated to have 3-20 wt.% of a low molecular weight fraction having a number average molecular weight M _n less than 35,000. The process for their preparation differs from that of EP-A-0 692 496 in that only 10-95% by weight of the alkylthiol before the polymerization into the monomer mixture are mixed and the remaining amount of the alkylthiol is added only when a polymerization conversion of 20-70 wt.% Is reached.

With regard to latex coagulation, in all three patent applications EP-A-0 692 496 . EP-A-0 779 301 and EP-A-0 779 300 discloses that any coagulants can be used. As inorganic coagulants, calcium chloride and aluminum chloride are mentioned and used. The focus is on nitrile rubbers which are substantially halogen-free and are obtained by conducting the latex coagulation in the presence of a nonionic surfactant and using halogen-free metal salts such as aluminum sulfate, magnesium sulfate and sodium sulfate. As preferred, the coagulation is indicated using aluminum sulfate or magnesium sulfate. The resulting substantially halogen-free nitrile rubber has a halogen content of not more than 3 ppm.

In Comparative Example 6 of EP-A-779300 or Comparative Example 7 of EP-A-0 779 301 For example, latex coagulation is performed with a mixture of NaCl and CaCl ₂ using CaCl ₂ in large quantities and the weight ratio of NaCl and CaCl _{2 being} 1: 0.75. With respect to the scorch time and the stress value at 100% elongation no significant differences are found in comparison to the other examples given in the respective tables 12 and 13, respectively.

For the preparation of these nitrile rubbers, it is according to EP-A-0 692 496 . EP-A-0 779 300 such as EP-A-0 779 301 It is essential that alkylthiols in the form of the compounds 2,2,4,6,6-pentmethylheptane-4-thiol and 2,2,4,6,6,8,8-heptamethylnonan-4-thiol are used as molecular weight regulators. It is clearly pointed out that when using the conventional known tert-dodecyl mercaptan nitrile rubbers with poorer properties are obtained as regulators.

For the in EP-A-0 692 496 . EP-A-0 779 300 such as EP-A-0 779 301 Nitrile rubbers produced are claimed to possess a favorable property profile, good processability of the rubber compounds and low mold contamination during processing. The resulting vulcanizates should have a good combination of low temperature and oil resistance and have good mechanical properties. It is further asserted that at the production of nitrile rubbers by high polymerization conversions of greater than 75%, preferably greater than 80% high productivity can be achieved and also the vulcanization rate in the vulcanization with sulfur or peroxides is high, especially in NBR types for injection molding. It is further stated that the nitrile rubbers have a short scorch time and a high crosslink density. About the property of storage stability is made in the said patent applications no statement.

In summary, it has to be said that to date no process has been described which enables the synthesis of nitrile rubbers which predictably have a good storage stability.

The object of the present invention was thus to provide nitrile rubbers which have a good storage stability and at the same time have good properties during processing, ie a good vulcanization profile.

• (i) einen Calcium-Gehalt von mindestens 150 ppm, bezogen auf den Nitrilkautschuk, und einen Chlor-Gehalt von mindestens 40 ppm, bezogen auf den Nitrilkautschuk, aufweist, und
• (ii) der 2,2,4,6,6-Pentamethylheptan-4-thio- und/oder 2,4,4,6,6-Pentamethylheptan-2-thio- und/oder 2,3,4,6,6-Pentamethylheptan-2-thio und/oder 2,3,4,6,6-Pentamethylheptan-3-thio-Endgruppen enthält.

The invention relates to a nitrile rubber which contains repeating units of at least one α, β-unsaturated nitrile, at least one conjugated diene and optionally one or more further copolymerizable monomers and the

• (I) has a calcium content of at least 150 ppm, based on the nitrile rubber, and a chlorine content of at least 40 ppm, based on the nitrile rubber, and,
• (ii) the 2,2,4,6,6-pentamethylheptane-4-thio and / or 2,4,4,6,6-pentamethylheptane-2-thio and / or 2,3,4,6, Contains 6-pentamethylheptane-2-thio and / or 2,3,4,6,6-pentamethylheptane-3-thio end groups.

For the determination of the calcium content , the following method has been used and is used in the context of this invention: 0.5 g of the nitrile rubbers are digested by dry ashing at 550 ° C. in a platinum crucible with subsequent dissolution of the ash in hydrochloric acid. After appropriate dilution of the digestion solution with deionized water, the calcium content is determined by ICP-OES (inductively coupled plasma-optical emission spectrometry) at a wavelength of 317.933 nm against calibration matrix adapted calibration solutions. Depending on the concentration of the elements in the digestion solution or sensitivity of the measuring instrument used, the concentrations of the sample solutions for the respective wavelengths used are adapted to the linear range of the calibration ( B. Welz "Atomic Absorption Spectrometry", 2nd ed., Verlag Chemie, Weinheim 1985 )

The nitrile rubbers according to the invention preferably have a calcium content of at least 200 ppm, more preferably of at least 400 ppm, most preferably of more than 500 ppm, in particular of at least 600 ppm and more preferably of at least 800 ppm of calcium, based on the nitrile rubber.

Surprisingly, the nitrile rubbers according to the invention have the desired very good storage stability and at the same time have a positive processing behavior.

Storage stability of a rubber is understood to mean the greatest possible constancy of the molecular weight or Mooney viscosity over a relatively long period of time, and in particular also at relatively high temperatures.

The storage stability is usually determined by storing the unvulcanized nitrile rubber at a higher temperature over a defined period of time (also referred to as hot air storage) and determining the difference in Mooney viscosities before and after this storage at elevated temperature. Since the Mooney Viscosity of nitrile rubber usually increases in the hot air storage, the storage stability is characterized by the difference in Mooney viscosity after storage minus Mooney viscosity before storage.

worin

MV1

den Wert für die Mooney-Viskosität eines Nitrilkautschuks und

MV2

den Wert für die Mooney-Viskosität desselben Nitrilkautschuks nach einer 48 stündigen Lagerung bei 100°C darstellt

The storage stability is thus given by the following formula (I) $$\mathrm{LS}=\mathrm{MV}2-\mathrm{MV}1$$

wherein

MV1

the value for the Mooney viscosity of a nitrile rubber and

MV2

represents the value of the Mooney viscosity of the same nitrile rubber after 48 hours storage at 100 ° C

The values for the Mooney viscosity (ML 1 + 4 @ 100 ° C.) are determined in each case by means of a shear disk viscometer in accordance with DIN 53523/3 or ASTM D 1646 at 100 ° C.

It has been proven to carry out the 48-hour storage of nitrile rubber at 100 ° C in a convection oven, the oxygen content in this convection oven compared to normal air is unchanged.

Sufficiently stable in storage is a nitrile rubber, if the storage stability LS is a maximum of 5 Mooney units. Preferably, LS is less than 5 Mooney units, more preferably at most 4 Mooney units.

NBR:

The nitrile rubbers according to the invention have repeating units of at least one α, β-unsaturated nitrile, at least one conjugated diene and optionally one or more further copolymerizable monomers.

The conjugated diene can be of any nature. Preference is given to using (C ₄ -C ₆ ) -conjugated dienes. Particular preference is given to 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, piperylene, 1,3-pentadiene or mixtures thereof. Particular preference is given to 1,3-butadiene and isoprene or mixtures thereof. Very particular preference is given to 1,3-butadiene.

As α, β-unsaturated nitrile, any known α, β-unsaturated nitrile can be used, preferred are (C ₃ -C ₅ ) -α, β-unsaturated nitriles such as acrylonitrile, methacrylonitrile, 1-chloroacrylonitrile, ethacrylonitrile or mixtures thereof. Particularly preferred is acrylonitrile.

A particularly preferred nitrile rubber is thus a copolymer of acrylonitrile and 1,3-butadiene.

In addition to the conjugated diene and the α, β-unsaturated nitrile, one or more other copolymerizable monomers may be used, e.g. α, β-unsaturated mono- or dicarboxylic acids, their esters or amides. Such nitrile rubbers are also commonly referred to as carboxylated nitrile rubbers or, for brevity, "XNBR".

As α, β-unsaturated mono- or dicarboxylic acids, for example, fumaric acid, maleic acid, acrylic acid, methacrylic acid, crotonic acid and itaconic acid can be used. Preference is given to maleic acid, acrylic acid, methacrylic acid and itaconic acid.

Examples of esters of the α, β-unsaturated carboxylic acids are alkyl esters, alkoxyalkyl esters, hydroxyalkyl esters or mixtures thereof.

Particularly preferred alkyl esters of the α, β-unsaturated carboxylic acids are methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate , 2-Ethlyhexyl (meth) acrylate, octyl (meth) acrylate and lauryl (meth) acrylate. In particular, n-butyl acrylate is used.

Particularly preferred alkoxyalkyl esters of the α, β-unsaturated carboxylic acids are methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate and methoxyethyl (meth) acrylate. In particular, methoxyethyl acrylate is used.

Particularly preferred hydroxyalkyl esters of the α, β-unsaturated carboxylic acids are hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate and hydroxy (butyl (meth) acrylate.

Other suitable esters of the α, β-unsaturated carboxylic acids are, for example, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, glycidyl (meth) acrylate, epoxy (meth) acrylate and urethane (meth) acrylate.

Further possible monomers are vinylaromatics such as styrene, α-methylstyrene and vinylpyridine.

The proportions of conjugated diene and α, β-unsaturated nitrile in the nitrile rubbers according to the invention can vary within wide limits. The proportion of or the sum of the conjugated dienes is usually in the range of 20 to 95 wt.%, Preferably in the range of 40 to 90 wt .-%, particularly preferably in the range of 60 to 85 wt.%, Based on the total polymer. The proportion of or the sum of the α, β-unsaturated nitriles is usually from 5 to 80% by weight, preferably from 10 to 60% by weight, more preferably from 15 to 40% by weight, based on the total polymer. The proportions of the monomers in each case add up to 100% by weight.

The additional monomers can be present in amounts of from 0 to 40% by weight, preferably from 0.1 to 40% by weight, particularly preferably from 1 to 30% by weight, based on the total polymer. In this case, corresponding proportions of the conjugated dienes and / or of the α, β-unsaturated nitriles are replaced by the proportions of these additional monomers, wherein the proportions of all monomers continue to add up to 100 wt .-%.

If esters of (meth) acrylic acid are used as additional monomers, this usually takes place in amounts of from 1 to 25% by weight.

If α, β-unsaturated mono- or dicarboxylic acids are used as additional monomers, this is usually carried out in amounts of less than 10% by weight.

The nitrogen content is determined in the nitrile rubbers according to the invention according to DIN 53 625 according to Kjeldahl. Due to the content of polar comonomers, the nitrile rubbers are usually soluble in methyl ethyl ketone at 20 ° C ≥ 85 wt.%.

The nitrile rubbers have Mooney values (ML (1 + 4 @ 100 ° C.)) of from 10 to 150, preferably from 20 to 100 Mooney units, more preferably from 25 to 60 Mooney units. This is the value MV1 in the sense of the formula (I).

The glass transition temperatures of the nitrile rubbers are in the range -70 ° C to + 10 ° C, preferably in the range -60 ° C to 0 °

Preference is given to nitrile rubbers according to the invention which have repeating units of acrylonitrile, 1,3-butadiene and optionally one or more further copolymerisable monomers. Likewise preferred are nitrile rubbers, the repeat units of acrylonitrile, 1,3-butadiene and one or more α, β-unsaturated mono- or dicarboxylic acid, their esters or amides, and in particular repeat units of an alkyl ester of an α, β-unsaturated carboxylic acids, very particularly preferably methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Octyl (meth) acrylate or lauryl (meth) acrylate.

The nitrile rubber according to the invention preferably comprises 2,2,4,6,6-pentamethylheptane-4-thio, 2,4,4,6,6-pentamethylheptane-2-thio, 2,3,4,6,6-pentamethyl heptane-2-thio and 2,3,4,6,6-pentamethylheptane-3-thio end groups.

• (i) die Emulsionspolymerisation in Gegenwart eines Gemischs enthaltend 2,2,4,6,6-Pentamethylheptanthiol-4, 2,4,4,6,6-Pentamethylheptanthiol-2, 2,3,4,6,6-Pentamethylheptanthiol-2 und 2,3,4,6,6-Pentamethylheptanthiol-3 durchgeführt wird,
• (ii) der nach der Polymerisation anfallende, den Nitrilkautschuk enthaltende Latex einer Koagulation unter Einsatz mindestens eines Salzes ausgewählt aus der Gruppe bestehend aus Aluminium-, Calcium-, Magnesium-, Natrium-, Kalium- und Lithium-Salzen, unterworfen wird,
• (iii) entweder bei der Koagulation ein wasserlösliches Calcium-Salz anwesend ist und/oder die Wäsche des koagulierten Nitrilkautschuks mit calciumionenhaltigem Wasser durchgeführt wird und
• (iv) entweder bei der Emulsionspolymerisation, bei der Koagulation oder bei der nachfolgenden Wäsche des koagulierten Nitrilkautschuks ein Salz auf Basis eines Chlorids anwesend ist.

The present invention further provides a process for the preparation of nitrile rubbers by emulsion polymerization of at least one α, β-unsaturated nitrile, at least one conjugated diene and optionally one or more other copolymerizable monomers, wherein the first obtained in the polymerization, the nitrile rubber-containing latex coagulation and the resulting coagulated nitrile rubber is subsequently washed, characterized in that

• (i) the emulsion polymerization in the presence of a mixture comprising 2,2,4,6,6-pentamethylheptanethiol-4, 2,4,4,6,6-pentamethylheptanethiol-2,3,3,4,6,6-pentamethylheptanethiol 2 and 2,3,4,6,6-pentamethylheptanethiol-3 is carried out,
• (ii) subjecting the post-polymerization nitrile rubber-containing latex to coagulation using at least one salt selected from the group consisting of aluminum, calcium, magnesium, sodium, potassium and lithium salts;
• (iii) either a water-soluble calcium salt is present during coagulation and / or the scrubbing of the coagulated nitrile rubber is carried out with calcium-ion containing water, and
• (iv) a salt based on a chloride is present either in the emulsion polymerization, in the coagulation or in the subsequent washing of the coagulated nitrile rubber.

Process for the preparation of nitrile rubbers :

The preparation of the nitrile rubbers takes place in the process according to the invention by emulsion polymerization.

As emulsifiers water-soluble salts of anionic emulsifiers or neutral emulsifiers can be used. Anionic emulsifiers are preferably used.

Modified resin acids obtained by dimerization, disproportionation, hydrogenation and modification of resin acid mixtures containing abietic acid, neoabietic acid, palustric acid, levopimaric acid can be used as anionic emulsifiers. A particularly preferred modified rosin acid is the disproportionated rosin acid ( Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition, Volume 31, pp. 345-355 ).

As anionic emulsifiers and fatty acids can be used. These contain 6 to 22 C atoms per molecule. They can be fully saturated or contain one or more double bonds in the molecule. Examples of fatty acids are caproic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid. The carboxylic acids are usually based on origin-specific oils or fats such. Castoroil, cottonseed, peanut oil, linseed oil, coconut fat, palm kernel oil, olive oil, rapeseed oil, soybean oil, fish oil and beef tallow, etc. ( Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition, Vol. 13, pp. 75-108 ). Preferred carboxylic acids are derived from coconut fatty acid and beef tallow and are partially or completely hydrogenated.

Such carboxylic acids based on modified resin acids or fatty acids are used as water-soluble lithium sodium, potassium and ammonium salts. The sodium and potassium salts are preferred.

Anionic emulsifiers are also sulfonates, sulfates and phosphates bonded to an organic radical. Suitable organic radicals are aliphatic, aromatic, alkylated aromatics, fused aromatics, and methlyene-bridged aromatics, wherein the methylene-bridged and fused aromatics may additionally be alkylated. The length of the alkyl chains is 6 to 25 C atoms. The length of the alkyl chains bonded to the aromatics is between 3 and 12 C atoms.

The sulfates, sulfonates and phosphates are used as lithium, sodium, potassium and ammonium salts. The sodium, potassium and ammonium salts are preferred.

Examples of such sulfonates, sulfates and phosphates are Na lauryl sulfate, Na alkyl sulfonate, Na alkylarylsulfonate, Na salts methylenverbrückter arylsulfonates, Na salts of alkylated naphthalenesulfonates and the Na salts of methlyenverbrückter Napthalinsulfonate, also may be oligomerized, wherein the Otigimerisierungsgrad lies between 2 to 10. Usually, the alkylated naphthalenesulfonic acids and the methylene-bridged (and optionally alkylated) naphthalenesulfonic acids are present as mixtures of isomers, which may also contain more than 1 sulfonic acid group (2 to 3 sulfonic acid groups) in the molecule. Particular preference is given to Na lauryl sulfate, Na alkylsulfonate mixtures having 12 to 18 C atoms, Na alkylaryl sulfonates, Na diisobutylene naphthalene sulfonate, methylene-bridged polynaphthalene sulfonate mixtures and methylene-bridged aryl sulfonate mixtures.

Neutral emulsifiers are derived from addition products of ethylene oxide and propylene oxide on compounds with sufficiently acidic hydrogen. These include, for example, phenol, alkylated phenol and alkylated amines. The average degrees of polymerization of the epoxides are between 2 and 20. Examples of neutral emulsifiers are ethoxylated nonylphenols having 8, 10 and 12 ethylene oxide units. The neutral emulsifiers are usually not used alone, but in combination with anionic emulsifiers.

Preference is given to the Na and K salts of disproportionated abietic acid and partially hydrogenated tallow fatty acid, and also mixtures thereof, sodium lauryl sulfate, Na alkylsulfonates, sodium alkylbenzenesulfonate and alkylated and methylene-bridged naphthalenesulfonic acids.

The emulsifiers are used in an amount of 0.2 to 15 parts by weight, preferably 0.5 to 12.5 parts by weight, particularly preferably 1.0 to 10 parts by weight, based on 100 parts by weight of the monomer mixture used.

The emulsion polymerization is carried out using the emulsifiers mentioned. If, after completion of the polymerization, latices are obtained which tend to premature self-coagulation due to a certain instability, the said emulsifiers can also be used for the post-stabilization of the latices. This may be necessary in particular before removal of unreacted monomers by treatment with water vapor and before latex storage.

• 2,2,4,6,6-Pentamethylheptanthiol-4,
• 2,4,4,6,6-Pentamethylheptanthiol-2,
• 2,3,4,6,6-Pentamethylheptanthiol-2 und
• 2,3,4,6,6-Pentamethylheptanthiol-3,

enthält. Dieses Gemisch von C₁₂-Mercaptanen dient zur Molekulargewichtsregelung des entstehenden Nitrilkautschuks. Eine detaillierte Beschreibung dieses Gemischs und eines Verfahren zu seiner Herstellung findet sich in einer am gleichen Tag eingereichten Anmeldung der Lanxess Deutschland GmbH.The process according to the invention is carried out in the presence of a mixture which

• 2,2,4,6,6-pentamethylheptane-4,
• 2,4,4,6,6-pentamethylheptane-2,
• 2,3,4,6,6-pentamethylheptanethiol-2 and
• 2,3,4,6,6-pentamethylheptane-3,

contains. This mixture of C ₁₂ -mercaptans serves to control the molecular weight of the resulting nitrile rubber. A detailed description of this mixture and a method for its Production is found in an application filed on the same day by Lanxess Deutschland GmbH.

The aforesaid mixture for controlling the molecular weight of the nitrile rubber is used in amounts of from 0.05 to 3 parts by weight, preferably from 0.1 to 1.5 parts by weight, based on 100 parts by weight of the monomer mixture.

The metering of the mixture for controlling the molecular weight is carried out either at the beginning of the polymerization or in portions during the polymerization, with the portionwise addition of all and also individual components of the regulator mixture during the polymerization being preferred. Preferably, the nitrile rubber in this case, 2,2,4,6,6-pentamethylheptane-4-thio, 2,4,4,6,6-pentamethylheptane-2-thio, 2,3,4,6,6 Pentamethylheptan-2-thio and 2,3,4,6,6-pentamethylheptane-3-thio end groups.

To initiate the emulsion polymerization typically polymerization initiators are used which decompose into radicals. These include compounds containing one -OO unit (peroxo compounds) or one -N≡N unit (azo compound).

The peroxo compounds include hydrogen peroxide, peroxodisulfates, peroxodiphosphates, hydroperoxides, peracids, peracid esters, peracid anhydrides and peroxides having two organic radicals. As salts of peroxodisulfuric acid and peroxodiphosphoric acid, sodium, potassium and ammonium salts can be used. Suitable hydroperoxides are e.g. t-butyl hydroperoxide, cumene hydroperoxide and p-menthane hydroperoxide. Suitable peroxides having two organic radicals are dibenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide, dicumyl peroxide, t-butyl perbenzoate, t-butyl peracetate, etc. Suitable azo compounds are azobisisobutyronitrile, azobisvaleronitrile and azobiscyclohexanenitrile.

Hydrogen peroxide, hydroperoxides, peracids, peracid esters, peroxodisulfate and peroxodiphosphate are also used in combination with reducing agents. Suitable reducing agents are sulfenates, sulfinates, sulfoxylates, dithionite, sulfite, metabisulfite, disulfite, sugars, urea, thiourea, xanthates, thioxanthogenates, hydrazinium salts, amines and amine derivatives such as aniline, dimethylaniline, monoethanolamine, diethanolamine or triethanolamine. Initiator systems consisting of an oxidizing and a reducing agent are called redox systems. When using redox systems are often used in addition salts of transition metal compounds such as iron, cobalt or nickel in combination with suitable complexing agents such as sodium ethylenediamtetraacetat, sodium nitrilotriacetate and trisodium phosphate or Tetrakaliumdiphsophat.

Preferred redox systems are, for example: 1) potassium peroxodisulfate in combination with triethanolamine, 2) ammonium peroxodiphosphate in combination with sodium metabisulfite (Na ₂ S ₂ O ₅ ), 3) p-menthane hydroperoxide / sodium formaldehyde sulfoxylate in combination with Fe-II sulfate (FeSO ₄ .7H ₂ O), sodium ethylenediaminoacetate and trisodium phosphate; 4) cumene hydroperoxide / sodium formaldehyde sulfoxylate in combination with Fe-II sulfate (FeSO ₄ .7H ₂ O), sodium ethylenediaminoacetate and tetrapotassium diphosphate.

The amount of oxidizing agent is 0.001 to 1 part by weight based on 100 parts by weight of monomer. The molar amount of reducing agent is between 50% to 500% based on the molar amount of the oxidizing agent used.

The molar amount of complexing agent refers to the amount of transition metal used and is usually equimolar with this.

To carry out the polymerization, all or individual components of the initiator system are metered in at the beginning of the polymerization or during the polymerization.

The addition in portions of all and also individual components of the initiator system during the polymerization is preferred. By sequential addition, the reaction rate can be controlled.

The polymerization time is in the range of 5 h to 15 h and depends essentially on the acrylonitrile content of the monomer mixture and on the polymerization temperature.

The polymerization temperature is in the range of 0 to 30 ° C, preferably in the range of 5 to 25 ° C.

When conversions in the range of 50 to 90%, preferably in the range of 70 to 85%, are achieved, the polymerization is stopped.

For this purpose, a stopper is added to the reaction mixture. Suitable for this purpose are, for example, dimethyldithiocarbamate, Na nitrite, mixtures of dimethyldithiocarbamate and Na nitrite, hydrazine and hydroxylamine, and salts derived therefrom, such as hydrazinium sulfate and hydroxylammonium sulfate, diethylhydroxylamine, diisopropylhydroxylamine, water-soluble salts of Hydroquinone, sodium dithionite, phenyl-α-naphthylamine and aromatic phenols such as tert-butyl catechol, or phenothiazine.

The amount of water used in the emulsion polymerization is in the range of 100 to 900 parts by weight, preferably in the range of 120 to 500 parts by weight, more preferably in the range of 150 to 400 parts by weight of water based on 100 parts by weight the monomer mixture.
In the emulsion polymerization, salts may be added to the aqueous phase to reduce the viscosity during the polymerization, for pH adjustment as well as for pH buffering. For this purpose, it is customary to use salts of monovalent metals in the form of potassium and sodium hydroxide, sodium sulfate, sodium carbonate, sodium bicarbonate, lithium chloride, sodium chloride and potassium chloride. Preference is given to sodium and potassium hydroxide, sodium bicarbonate, lithium, sodium and potassium chloride. The amounts of these electrolytes are in the range 0 to 1 parts by weight, preferably 0 to 0.5 parts by weight based on 100 parts by weight of the monomer mixture. The addition of a chloride-containing salt during the emulsion polymerization is necessary if neither in the subsequent coagulation nor in the subsequent washing of the coagulated nitrile rubber, a chloride-containing salt is to be used (feature (iv) of the inventive method).

The polymerization can be carried out either batchwise or continuously in a stirred tank cascade.

To achieve a uniform course of polymerization, only part of the initiator system is used for the start of the polymerization, and the remainder is metered in during the polymerization. Usually, the polymerization is started with 10 to 80% by weight, preferably 30-50% by weight, of the total amount of initiator. The addition of individual components of the initiator system is possible.

If you want to produce chemically uniform products, acrylonitrile or butadiene are postdosed, if the composition is outside the azeotropic butadiene / acrylonitrile ratio. Preference is given to replenishing with NBR types having acrylonitrile contents of from 10 to 34 and with types containing from 40 to 50% by weight of acrylonitrile ( W. Hofmann, Rubber Chem. Technol. 36 (1963) 1 ) the case. The replenishment takes place - as in the DD 154 702 indicated - preferably computer-controlled on the basis of a computer program.

To remove unreacted monomers and volatile components of the stopped latex is subjected to a steam distillation. In this case, temperatures in the range of 70 ° C to 150 ° C are used, wherein at temperatures <100 ° C, the pressure is reduced.

Before the removal of the volatile constituents, a post-stabilization of the latex with emulsifier can take place. For this purpose, it is expedient to use the abovementioned emulsifiers in amounts of 0.1 to 2.5% by weight, preferably 0.5 to 2.0% by weight. % based on 100 parts by weight of nitrile rubber.

Latex coagulation:

Before or during latex coagulation one or more anti- aging agents can be added to the latex. For this purpose, phenolic, aminic and other anti-aging agents are suitable.

Suitable phenolic antioxidants are alkylated phenols, styrenated phenol, hindered phenols such as 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol (BHT), 2,6-di-tert. Butyl-4-ethylphenol, sterically hindered phenols containing ester groups, thioether-containing sterically hindered phenols, 2,2'-methylenebis (4-methyl-6-tert-butylphenol) (BPH) and sterically hindered thiobisphenols.

If a discoloration of the rubber is of no importance, also aminic aging inhibitor z. B. mixtures of diaryl-p-phenylenediamines (DTPD), octylated diphenylamine (ODPA), phenyl-α-naphthylamine (PAN), phenyl-β-naphthylamine (PBN), preferably those based on phenylenediamine used. Examples of phenylenediamines are N-isopropyl-N'-phenyl-p-phenylenediamine, N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD), N-1,4-dimethylpentyl-N'-phenylphenyl Phenylenediamine (7PPD), N, N'-bis-1,4- (1,4-dimethylpentyl) -p-phenylenediamine (77PD), etc.

Other anti-aging agents include phosphites such as tris (nonylphenyl) phosphite, polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), 2-mercaptobenzimidazole (MBI), methyl 2-mercaptobenzimidazole (MMBI), zinc methylmercaptobenzimidazole ( ZMMBI). The phosphites are generally used in combination with phenolic anti-aging agents. TMQ, MBI and MMBI are mainly used for NBR grades that are vulcanized peroxide.

For coagulation, the latex is used with a pH of at least 6, preferably of> 6. Optionally, this pH is adjusted by addition of a base, preferably of ammonia or sodium or potassium hydroxide.

The coagulation is carried out using at least one salt selected from the group consisting of aluminum, calcium, magnesium, sodium, potassium and lithium salts.

As anions of these salts usually monovalent or divalent anions are used. Preferred are halide, more preferably chloride, nitrate, sulfate, bicarbonate, carbonate, formate and acetate.

Suitable examples are sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium nitrate, potassium nitrate, sodium sulfate, potassium sulfate, sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, aluminum sulfate, potassium aluminum sulfate (potassium alum), sodium aluminum sulfate (sodium alum), sodium acetate, calcium acetate and calcium formate.

Important for the specific calcium content of the nitrile rubbers according to the invention is that either at least one water-soluble calcium salt is present in the latex coagulation or - if this is not the case - the subsequent washing of the coagulated nitrile rubber using non-deionized and thus calcium ion-containing water is carried out.

If a water-soluble calcium salt is used for latex coagulation, calcium chloride is preferred.

The concentration of the solution of one or more salts selected from the group consisting of aluminum, calcium, magnesium, sodium, potassium and lithium salts is 3 to 30 wt.%. For the preparation of the salt solution, water containing Ca ions is preferably used.

The total amount of salts necessary for the latex coagulation selected from the group consisting of aluminum, calcium, magnesium, sodium, potassium and lithium salts is 0.5-200% by weight, preferably 0.8-80% by weight. %, more preferably 1-50% by weight of salt, based on 100 parts by weight of nitrile rubber.

In addition to at least one salt selected from the group defined above, precipitants may also be used in the coagulation. Suitable precipitation aids are, for example, water-soluble polymers. These are nonionic, anionic or cationic.

Examples of nonionic polymeric precipitation aids are modified cellulose such as hydroxyalkyl cellulose or methyl cellulose and adducts of ethylene oxide and propylene oxide on compounds with acidic hydrogen. Examples of compounds with acidic hydrogen are: Fatty acid, sugars such as sorbitol, mono- and di-fatty acid glycerides, phenol, alkylated phenols, (alkyl) phenol / formaldehyde condensates, etc. The addition products of ethylene oxide and propylene oxide to these compounds may be random and block-like. Of these products, those in which solubility decreases with increasing temperature are preferred. Characteristic turbidity temperatures are in the range 0 to 100 ° C, in particular in the range of 20 to 70 ° C.

Examples of anionic polymeric precipitation aids are the homopolymers and copolymers of (meth) acrylic acid, maleic acid, maleic anhydride, etc. The sodium salt of polyacrylic acid is preferred.

Cationic polymeric precipitation aids are usually based on polyamines and on homo- and copolymers of (meth) acrylamide. Preference is given to polymethacxrylamides and polyamines, in particular based on epichlorohydrin and dimethylamine.

The amounts of polymeric precipitation aids are 0.01 to 5 parts by weight, preferably 0.05 to 2.5 parts by weight per 100 parts by weight of nitrile rubber.

The use of other precipitation aids is conceivable. It should be noted, however, that it is possible without problems, the inventive method with the desired success in the absence of additional precipitation aids, and in particular in the absence of C ₁ -C ₄ alkylcelluloses, hydroxyalkylcelluloses, plant-derived proteinaceous materials or polysaccharides, such as Starch, or water-soluble polyamine compounds

The latex used for coagulation has expediently a solids concentration in the range of 1% to 40%, preferably in the range of 5% to 35% and particularly preferably in the range of 15 to 30% by weight.

The latex coagulation is carried out in the temperature range from 10 to 100 ° C. Preferably, the latex coagulation is carried out at a temperature of 20 to 90 ° C.

The latex coagulation can be continuous or discontinuous, preferably continuous.

Washing the coagulated nitrile rubber:

After coagulation, the nitrile rubber is usually present in the form of so-called crumbs. The laundry of the coagulated NBR is therefore also referred to as crumb laundry. For washing these coagulated crumbs, either deionized water (also referred to as "DW") may or may not be used Deionized water (also called "BW") can be used. If no calcium salt is present during the coagulation of the latex with at least one salt selected from the previously defined group of salts, the washing of the coagulated nitrile rubber should be carried out using non-deionized and therefore calcium ion-containing water.

The wash is stirred at a temperature in the range of 15 to 90 ° C, preferably at a temperature in the range of 20 to 80 ° C.

The amount of washing water is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, and more preferably 1 to 5 parts by weight, based on 100 parts by weight of nitrile rubber.

Preferably, the rubber crumbs are subjected to a multi-stage washing, wherein the rubber crumbs are partially dewatered between the individual washing stages. The residual moistures of the crumbs between the individual washing stages are in the range from 5 to 50% by weight, preferably in the range from 7 to 25% by weight. The number of washing stages is usually from 1 to 7, preferably from 1 to 3. The washing is carried out batchwise or continuously. Preference is given to using a multistage, continuous process, with countercurrent washing being preferred for the careful handling of water.

Water removal and drying:

After completion of the wash, it has been proven to dehydrate the nitrile rubber crumbs. This usually happens in two stages. In the first stage, the rubber crumbs are mechanically pre-dewatered. In the second stage, the remaining water is evaporated. Both the pre-dewatering and the drying are preferably carried out continuously. For mechanical pre-dewatering Seiherschnecken are suitable, in which the water is squeezed laterally over Seiherspalte or screws, where the mechanical dewatering takes place against the product flow (welding principle).

The adjustment of the cation contents remaining in the nitrile rubber may additionally and if desired be influenced by the degree of mechanical pre-dewatering. This is particularly appropriate when a so-called inefficient laundry is applied. Efficient laundry already provides the appropriate cation levels. The water contents after the mechanical pre-dewatering are in the range of 5 to 25 wt.%. For the adjustment of the cation mixture remaining in the product, it has been found that the water contents after mechanical pre-dewatering are 5 to 15% by weight, in particular 5 to 10% by weight.

The drying of the pre-dehydrated nitrile rubber takes place in a fluid bed dryer or in a plate dryer. The drying temperatures are between 80 and 150 ° C. Preference is given to drying with a temperature program, the temperature being lowered towards the end of the drying process.

Surprisingly, the nitrile rubbers according to the invention, which have the specified content of calcium and chlorine, have the desired high storage stability LS of a maximum of 5 Mooney units. The high storage stability already has positive effects during the drying of the nitrile rubber, since otherwise a certain aging of the rubber takes place involuntarily during this drying. The high storage stability facilitates the setting of a given target Mooney viscosity. This reduces the amount of non-conforming nitrile rubber. Furthermore, the high storage stability results in a reduction of the complaints that result from changing the Mooney viscosity during long storage or transport times. The rubbers according to the invention are suitable for the reproducible production of vulcanizable mixtures. The molded parts obtainable therefrom by vulcanization are thus also distinguished by a reproducible mechanical and physical property profile.

The invention therefore also relates to the use of the nitrile rubbers according to the invention for the production of vulcanizable mixtures containing at least one nitrile rubber according to the invention, at least one crosslinker and optionally further additives.

These vulcanizable mixtures are prepared by mixing at least one nitrile rubber according to the invention, at least one crosslinker and optionally further additives.

Suitable crosslinkers are, for example, peroxidic crosslinkers such as bis (2,4-dichlorobenzyl) peroxide, dibenzoyl peroxide, bis (4-chlorobenzoyl) peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcylohexane, tert Butyl perbenzoate, 2,2-bis (t-butylperoxy) butene, 4,4-di-tert-butyl peroxynonylvalerate, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, tert-butylcumyl peroxide, 1,3-bis (t-butylperoxy isopropyl) benzene, di-t-butyl peroxide and 2,5-dimethyl-2,5-di (t-butylperoxy) hexyn-3.

It may be advantageous, in addition to these peroxidic crosslinkers, to use further additives with the aid of which the crosslinking yield can be increased. For example, triallylisocyanurate, triallylcyanurate, trimethylolpropane tri (meth) acrylate, triallyltrimellithate, Ethylene glycol dimethacrylate, butanediol dimethacrylate, trimethylolpropane trimethacrylate, Zn diacrylate, Zn dimethacrylate, 1,2-polybutadiene or N, N'-m-phenylenedimaleimide.

The total amount of crosslinker (s) is usually in the range of 1 to 20 phr, preferably in the range of 1.5 to 15 phr and more preferably in the range of 2 to 10 phr, based on the nitrile rubber.

As crosslinkers it is also possible to use sulfur in elementary soluble or insoluble form or sulfur donors.

Suitable sulfur donors are, for example, dimorpholyl disulfide (DTDM), 2-morpholinodithiobenzothiazole (MBSS), caprolactam disulfide, dipentamethylene thiuram tetrasulfide (DPTT), and tetramethylthiuram disulfide (TMTD).

Even in the case of sulfur vulcanization of the nitrile rubbers according to the invention, it is possible to use further additives with the aid of which the crosslinking yield can be increased. In principle, however, the crosslinking can also take place with sulfur or sulfur donors alone.

Conversely, however, the crosslinking of the nitrile rubbers according to the invention can also be carried out only in the presence of the abovementioned additives, i. without the addition of elemental sulfur or sulfur donors.

As additives with the aid of which the crosslinking yield can be increased, e.g. Dithiocarbamates, thiurams, thiazoles, sulfenamides, xanthogenates, guanidine derivatives, caprolactams and thiourea derivatives.

As dithiocarbamates can be used, for example: ammonium dimethyldithiocarbamate, sodium diethyldithiocarbamate (SDEC), Natriumdibutyl-dithiocarbamate (SDBC), zinc dimethyldithiocarbamate (ZDMC), zinc diethyldithiocarbamate (ZDEC), Zinkdibutyldithio-carbamate (ZDBC), zinc ethylphenyldithiocarbamate (ZEPC), zinc dibenzyldithiocarbamate (ZBEC), zinc pentamethylenedithiocarbamate ( Z5MC), tellurium diethyldithio-carbamate, nickel dibutyldithiocarbamate, nickel dimethyldithiocarbamate and zinc diisononyldithio-carbamate.

As thiurams, there may be used, for example, tetramethylthiuram disulfide (TMTD), tetramethylthiuram monosulfide (TMTM), dimethyldiphenylthiuram disulfide, tetrabenzylthiuram disulfide, dipentamethylenethiuram tetrasulfide and tetraethylthiuram disulfide (TETD). As thiazoles, there may be used, for example, 2-mercaptobenzothiazole (MBT), dibenzothiazyl disulfide (MBTS), zinc mercaptobenzothiazole (ZMBT) and copper 2-mercaptobenzothiazole.

Examples of sulfenamide derivatives which can be used are: N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N-tert-butyl-2-benzthiazyl sulfenamide (TBBS), N, N'-dicyclohexyl-2-benzthiazyl sulfenamide (DCBS), 2-morpholinothiobenzothiazole (MBS), N-Oxydiethylenethiocarbamyl-N-tert-butylsulfenamide and Oxydiethylenethiocarbamyl-N-oxyethylene-sulfenamide.

As xanthates, there may be used, for example, sodium dibutylxanthogenate, zinc isopropyldibutylxanthogenate and zinc dibutylxanthogenate.

As guanidine derivatives can be used, for example: diphenylguanidine (DPG), di-o-tolylguanidine (DOTG) and o-tolylbiguanide (OTBG).

Examples of dithiophosphates which can be used are: zinc dialkydithiophosphates (chain length of the alkyl radicals C ₂ to C ₁₆ ), copper dialkyldithiophosphates (chain length of the alkyl radicals C ₂ to C ₁₆ ) and dithiophosphoryl polysulfide.

As caprolactam, for example, dithio-bis-caprolactam can be used.

As thiourea derivatives, for example, N, N'-diphenylthiourea (DPTU), diethylthiourea (DETU) and ethylene thiourea (ETU) can be used.

Also suitable as additives are, for example: zinc diamine diisocyanate, hexamethylenetetramine, 1,3-bis (citraconimidomethyl) benzene and cyclic disulfanes.

The additives mentioned as well as the crosslinking agents can be used both individually and in mixtures. The following substances for crosslinking the nitrile rubbers are preferably used: sulfur, 2-mercaptobenzothiazole, tetramethylthiuram disulfide, tetramethylthiuram monosulfide, zinc dibenzyldithiocarbamate, dipentamethylenethiuram tetrasulfide, Zinkdialkydithiophosphat, dimorpholyl, tellurium diethyldithiocarbamate, nickel dibutyldithiocarbamate, zinc dibutyldithiocarbamate, zinc dimethyldithiocarbamate and dithio-bis-caprolactam.

The crosslinking agents and aforementioned additives can each be used in amounts of about 0.05 to 10 phr, preferably 0.1 to 8 phr, in particular 0.5 to 5 phr (single dose, in each case based on the active substance).

In the case of the sulfur crosslinking according to the invention, it may also be expedient to use, in addition to the crosslinking agents and the abovementioned additives, further inorganic or organic substances, for example: zinc oxide, zinc carbonate, lead oxide, magnesium oxide, saturated or unsaturated organic fatty acids and their zinc salts, polyalcohols, Amino alcohols such as triethanolamine and amines such as dibutylamine, dicyclohexylamine, cyclohexylethylamine and polyetheramines.

In addition, scorch retarders can also be used. These include cyclohexylthiophthalimide (CTP), N, N'-dinitrosopentamethylenetetramine (DNPT), phthalic anhydride (PTA) and diphenylnitrosamine. Cyclohexylthiophtalimide (CTP) is preferred.

In addition to the addition of the crosslinker (s), the nitrile rubber of the invention may also be mixed with other customary rubber additives.

These include, for example, typical and well-known substances such as fillers, filler activators, antiozonants, antiaging agents, antioxidants, processing aids, extender oils, plasticizers, reinforcing materials and mold release agents.

As fillers , for example, carbon black, silica, barium sulfate, titanium dioxide, zinc oxide, calcium oxide, calcium carbonate, magnesium oxide, alumina, iron oxide, aluminum hydroxide, magnesium hydroxide, aluminum silicates, diatomaceous earth, talc, kaolins, bentonites, carbon nanotubes, Teflon (the latter preferably in powder form), or Silicates are used.

Suitable filler activators are, in particular, organic silanes, for example vinyltrimethyloxysilane, vinyldimethoxymethylsilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, N-cyclohexyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, isooctyltrimethoxysilane, isooctyltriethoxysilane Hexadecyltrimethoxysilane or (octadecyl) methyldimethoxysilane into consideration. Further filler activators are, for example, surfactants such as triethanolamine and ethylene glycols having molecular weights of 74 to 10,000 g / mol. The amount of filler activators is usually 0 to 10 phr based on 100 phr of the nitrile rubber.

As anti-aging agents it is possible to add to the vulcanizable mixtures those already described in connection with the latex coagulation in this application. she are usually used in amounts of about 0 to 5 phr, preferably 0.5 to 3 phr, based on 100 phr of the nitrile rubber.

Suitable mold release agents are, for example: saturated and partially unsaturated fatty and oleic acids and derivatives thereof (fatty acid esters, fatty acid salts, fatty alcohols, fatty acid amides) which are preferably used as a mixing component, furthermore products which can be applied to the mold surface, for example products based on low molecular weight silicone compounds , Products based on fluoropolymers and products based on phenolic resins.

The mold release agents are used as a blend component in amounts of about 0 to 10 phr, preferably 0.5 to 5 phr, based on 100 phr of the nitrile rubber.

Also the reinforcement with strength members (fibers) made of glass, according to the doctrine of US Patent No. 4,826,721 is possible as well as the reinforcement by cords, fabrics, fibers of aliphatic and aromatic polyamides (Nylon®, Aramid®), polyesters and natural fiber products.

The invention further provides a process for the production of moldings based on at least one nitrile rubber according to the invention, which comprises vulcanizing the vulcanizable mixture described above in a molding process, preferably using an injection molding process.

The invention thus also relates to the special molding which is obtainable by the aforementioned vulcanization process.

By this method a plurality of moldings can be made, e.g. a gasket, cap, tube or membrane. In particular, the nitrile rubbers according to the invention with the specific ion characteristic for producing an O-ring seal, a gasket, a shaft seal, a sealing collar, a sealing cap, a dust cap, a plug seal, a Thermoisolierschlauchs (with and without PVC additive), an oil cooler hose, one Air intake hose, a power steering hose or a pump diaphragm.

As an alternative to the direct production of moldings based on the nitrile rubber according to the invention, it is also possible that either (i) a metathesis reaction or (ii) a metathesis reaction and a subsequent hydrogenation or (iii) only one Hydrogenation connects. These metathesis or hydrogenation reactions are both well known to the skilled person and described in the literature.

For example, the metathesis is * WO-A-02/100941 as well as the WO-A-02/100905 known.

Hydrogenation can be carried out using homogeneous or heterogeneous hydrogenation catalysts. It is also possible to carry out the hydrogenation in situ, i. in the same reaction vessel in which optionally before the metathesis degradation was carried out and without need to isolate the degraded nitrile rubber. The hydrogenation catalyst is simply added to the reaction vessel.

The catalysts used are usually based on rhodium, ruthenium or titanium, but it is also possible to use platinum, iridium, palladium, rhenium, ruthenium, osmium, cobalt or copper either as metal or preferably in the form of metal compounds (see, for example, US Pat US-A-3,700,637 . DE-A-25 39 132 . EP-A-0 134 023 . DE-OS 35 41 689 . DE-OS 35 40 918 . EP-A-0 298 386 . DE-OS 35 29 252 . DE-OS 34 33 392 . US-A-4,464,515 and US-A-4,503,196 ).

Suitable catalysts and solvents for homogeneous phase hydrogenation are described below and are also exhaustive DE-A-25 39 132 and the EP-A-0 471 250 known

The selective hydrogenation can be achieved, for example, in the presence of a rhodium- or ruthenium-containing catalyst. It is possible, for example, to use a catalyst of the general formula

(R ¹ _m B) ₁ MX _n ,

wherein M is ruthenium or rhodium, R ^{1 are the} same or different and represent a C ₁ -C ₈ alkyl group, a C ₄ -C ₈ cycloalkyl group, a C ₆ -C ₁₅ aryl group or a C ₇ -C ₁₅ aralkyl group. B is phosphorus, arsenic, sulfur or a sulfoxide group S = O, X is hydrogen or an anion, preferably halogen and more preferably chlorine or bromine, 1 is 2,3 or 4, m is 2 or 3 and n is 1, 2 or 3, preferably 1 or 3. Preferred catalysts are tris (triphenylphosphine) rhodium (I) chloride, tris (triphenylphosphine) rhodium (III) chloride and tris (dimethyl sulfoxide) rhodium (III) chloride and tetrakis ( triphenylphosphine) rhodium hydride of the formula (C ₆ H ₅ ) ₃ P) ₄ RhH and the corresponding compounds in which the triphenylphosphine has been wholly or partly replaced by tricyclohexylphosphine. The catalyst can be used in small quantities. An amount in the range of 0.01-1% by weight, preferably in the range of 0.03-0.5% by weight, and more preferably in the range of 0.1-0.3% by weight based on the weight of the polymer are suitable.

It is usually useful to use the catalyst together with a co-catalyst which is a ligand of the formula R ¹ _m B, where R ¹ , m and B have the meanings given above for the catalyst. Preferably m is 3, B is phosphorus and the radicals R ¹ may be the same or different. Preference is given to co-catalysts with trialkyl, tricycloalkyl, Triaryl, triaralkyl, diaryl-monoalkyl, diaryl-monocycloalkyl, dialkyl-monoaryl, dialkylmonocycloalkyl, dicycloalkyl-monoaryl or dicyclalkyl-monoaryl-radicals.

Examples of co-catalysts can be found, for example, in US-A-4,631,315 , Preferred co-catalyst is triphenylphosphine. The co-catalyst is preferably used in amounts in a range of 0.3-5 wt.%, Preferably in the range of 0.5-4 wt.%, Based on the weight of the nitrile rubber to be hydrogenated. Furthermore, the weight ratio of the rhodium-containing catalyst to the cocatalyst is preferably in the range from 1: 3 to 1:55, particularly preferably in the range from 1: 5 to 1:45. Based on 100 parts by weight of the nitrile rubber to be hydrogenated, suitably 0.1 to 33 parts by weight of the co-catalyst, preferably 0.5 to 20 and most preferably 1 to 5 parts by weight, especially more than 2 but less than 5 parts by weight of co-catalyst based 100 parts by weight of the nitrile rubber to be hydrogenated.

The practical implementation of this hydrogenation is the expert from US-A-6,683,136 well known. It is usually carried out by subjecting the nitrile rubber to be hydrogenated in a solvent such as toluene or monochlorobenzene at a temperature in the range of 100 to 150 ° C and a pressure in the range of 50 to 150 bar for 2 to 10 hours with hydrogen.

In the context of this invention, hydrogenation is understood as meaning a conversion of the double bonds present in the starting nitrile rubber to at least 50%, preferably 70-100%, particularly preferably 80-100%.

When using heterogeneous catalysts are usually supported catalysts based on palladium, z. B. supported on carbon, silica, calcium carbonate or barium sulfate.

The optionally hydrogenated nitrile rubbers obtained after the metathesis and / or hydrogenation reaction of the nitrile rubbers according to the invention can be introduced into vulcanizable compositions analogously to the nitrile rubbers of the invention and used for the production of vulcanizates and moldings based on such vulcanizates. These optionally hydrogenated nitrile rubbers have Mooney viscosities (ML (1 + 4 @ 100 ° C)) of from 1 to 50, preferably from 1 to 40 Mooney units.

Examples I Preparation of NBR Latices A, B, C

The preparation of the NBR latexes A, B and C used in Examples 1) to 5) was carried out according to the base formulation given in Table 1, wherein all starting materials are stated in parts by weight based on 100 parts by weight of the monomer mixture. Table 1 also lists the respective polymerization conditions <b><u> Table 1: </ u></b> Latex no. A B C butadiene 73 81 56 acrylonitrile 27 12.5 / 6.5 44 Total amount of water 190 180 170 Erkantol ^® BXG ¹⁾ 3.69 3.69 3.69 Baykanol ^® PQ ²⁾ 1.10 1.10 1.10 K salt of coconut fatty acid 0.73 0.73 0.73 KOH 0.05 0.05 0.05 t-DDM ³⁾ 0.24 / 0.24 0.27 / 0.15 / 0.06 0.5 / 0.2 Potassium peroxodisulfate ⁴⁾ 0.39 / 0.19 0.45 / 0.20 0.27 Tris- (α-hydroxy-ethyl) -amine ⁵ ) 0.57 0.61 0.15 Na dithionite ⁶ ) 1.20 1.20 1.20 potassium hydroxide 1.28 1.28 1.28 Vulkanox.RTM ^® KB ⁷⁾ 1.25 1.25 1.25 Polymerization temperature [° C] 17 18 20 Polymerization conversion [%] 75 75 74.5 Polymerization time [h] 11 15 7.5 ¹⁾ Sodium salt of mono- and disulfonated naphthalenesulfonic acids containing isobutylene oligomer residues (Erkantol® BXG)
²⁾ sodium salt of methylene-bis-naphthalenesulfonate (Baykanol® PQ; Lanxess Deutschland GmbH)
³⁾ t-DDM: (tertiary dodecylmercaptan); Lanxess Germany GmbH
⁴⁾ Aldrich order no. : 21,622-4
⁵⁾ Aldrich order no. : T5,830-0
⁶⁾ Aldrich order no. : 15,795-3
⁷⁾ 2,6-di-tert-butyl-p-cresol; Lanxess Germany GmbH

Are in the above. Table 1 in one of the columns for the nitrile rubbers A, B and C indicated more than one value, this means that the entire amount of the respective feedstock was not added in one portion, but that a subsequent dosing (once or twice) took place. The sales at which this replenishment took place are given below.

The preparation of the NBR latex was carried out batchwise in a 2 m ³ autoclave with stirrer. The autoclave batches each used 350 kg of the monomer mixture and a total amount of water of 700 kg. From this amount of water, 650 kg with the emulsifiers (Erkantol ^® BXG, Baykanol ^® PQ and K salt of coconut fatty acid) and sodium hydroxide in an autoclave and rinsed with a stream of nitrogen. Thereafter, the destabilized monomers and the first indicated in Table 1 subset of the molecular weight regulator t-DDM were added and the reactor sealed. After the reactor contents were thermostated, the polymerizations were started by the addition of aqueous solutions of tris- (α-hydroxy-ethyl) -amine and potassium peroxodisulfate (at A and B, the first aliquot indicated in Table 1).

The course of the polymerization was followed by gravimetric conversion determinations. At a polymerization conversion of 15%, the residual quantities of potassium peroxodisulfate were replenished at A and B and the residual amount of t-DDM was replenished at A. When the yields given in Table 1 were reached, the polymerization was stopped by adding an aqueous solution of sodium dithionite and potassium hydroxide. Unreacted monomers and other volatiles were removed by steam distillation.

In the case of latex B, the addition of a total of 19 parts by weight of acrylonitrile was staggered: 12.5 parts by weight of acrylonitrile were initially charged in the reactor, and a further 6.5 parts by weight were metered in at a conversion of 35%. The addition of the t-DDM was also graded for latex B: 0.27 parts by weight of t-DDM were introduced into the reactor, 0.15 parts by weight were metered in at 20% conversion and 0.06 parts by weight were post-dosed at 40% conversion.

For latex C, the addition of the t-DDM was likewise staggered: 0.5 part by weight of t-DDM was introduced into the reactor, and 0.2 part by weight was replenished at 15% conversion.

The rubber latices or solid rubbers obtained had the following properties: Latex no. A B C Particle diameter (d50) [nm] 400 360 350 Solids content [% by weight] 20.5 22.8 24.8 PH value 8.4 11.4 10.9 Acrylonitrile content [wt. %] 28.9 18.8 38.6

Before coagulation of the respective NBR latex of this respectively with a 50% dispersion of Vulkanox ^® KB (1.25% Vulkanox ^® KB wt. Based on NBR solid) was added. The Vulkanox.RTM ^® -KB dispersion was prepared beforehand at 95-98 ° C by means of an Ultraturrax and comprised: 360 g Deionized water ("DW water") 40 g Ethoxylated nonylphenol (NP10 from Lanxess Deutschland GmbH) 400 g Vulkanox.RTM ^® KB

Variation of latex coagulation and crumb wash conditions was discontinuous on aliquots of latices A, B and C in a 100 liter stirrable, open container.

25 kg of latex were used for the latex coagulation, whereby the quantities of salts necessary for quantitative latex coagulation were determined in preliminary experiments. For the preparation of the salt solutions both deionized ("DW") and non-deionized and thus calcium ion-containing water ("BW") was used. The saline solutions were placed in the coagulation tank (salt type, concentration of salt solution, salt levels on NBR, coagulation temperature, etc. are listed in the tables below) before the latex was added with stirring. Latex coagulation was usually complete within a few minutes (<5 min). The amounts of salt were each designed so that the rubber crumbs were greater than 5 mm, so that they were not discharged in the subsequent crumb laundry. To carry out the crumb wash, the container had an inflow and outflow. On the inside of the container two rails were attached, so that the drainage could be shut off by means of a sieve (mesh size 2 mm) before carrying out the laundry, so the coagulated crumbs were not flushed out during the laundry. The washing was carried out in the experiments described here with a constant water flow rate of 200 l / h. For the wash, both deionized (DW) and non-deionized (BW) water was used. The resulting in the precipitation latex serum was not before the laundry from the Coagulation tank removed; ie the latex serum was removed by dilution washing. The framework conditions used for crumb washing (type of water, washing temperature, washing time, etc.) are listed in the following tables.

After completion of the laundry, the rubber crumbs were removed with a sieve, pre-dewatered in a Welding screw to a residual moisture of 5 to 20 wt.% And dried discontinuously in a circulating air dryer to a residual moisture content of <0, 6%.

The dried NBR rubbers were characterized by the Mooney viscosity before and after hot air storage for 48 hours at 100 ° C, i. the Mooney viscosity was determined once just after drying (i.e., before hot air storage) and then after 48 hours of hot melt aging at 100 ° C.

For the determination of the calcium content , 0.5 g of the nitrile rubbers were digested by dry ashing at 550 ° C. in a platinum crucible with subsequent dissolution of the ash in hydrochloric acid. After appropriate dilution of the digestion solution with deionized water, the calcium content was determined by inductively coupled plasma-optical emission spectrometry (OES) at a wavelength of 317.933 nm against acid matrix matched calibration solutions. Depending on the concentration of the elements in the digestion solution or the sensitivity of the measuring instrument used, the concentrations of the sample solutions for the respective wavelengths used were adapted to the linear range of the calibration ( B. Welz "Atomic Absorption Spectrometry", 2nd ed., Verlag Chemie, Weinheim 1985 )

The chlorine content of the nitrile rubbers according to the invention is determined as follows on the basis of DIN EN 14582, method A. The nitrile rubber sample is digested in a pressure vessel according to Parr in a melt of sodium peroxide and potassium nitrate. Sulfite solution is added to the resulting melt and acidified with sulfuric acid. In the solution thus obtained, the resulting chloride is determined by potentiometric titration with silver nitrate solution and calculated as chlorine.

Examples 1-10: (Inventive Examples and Comparative Examples) Storage stability of the nitrile rubber (28.9% by weight of acrylonitrile) obtained from latex A under the coagulation and washing conditions indicated in the following table.

The crumb wash was in all cases at 20 ° C and with deionized water (DW).

The comparative examples are identified by a "V" before the numbering. example Latex coagulation Washing time
[H] Chlorine content
[ppm] Ca
[ppm] mg
[ppm] ML (1 + 4 @ 100 ° C). [ME] pH of the latex type of salt Conc. Of saline solution
[Wt.%] Amount of salt on NBR
[Wt. %] T
[° C] MV1 MV2 LS 1 8.4 CaCl ₂ 0.6 6 20 3.8 110 1290 3 52 55 3 2 8.4 CaCl ₂ 1.2 12 20 3.5 108 1240 2 53 56 3 3 6.0 / HCl CaCl ₂ 1.2 12 20 3.5 100 1235 2 50 50 0 V4 6.0 / H ₂ SO ₄ MgCl ₂ 1.6 16 20 4.3 33 25 325 43 96 53 V5 8.4 _MgSO4 1.5 15 20 3.5 30 10 350 48 67 19 V6 6.0 / H ₂ SO _{4 MgSO4} 1.0 10 20 2.5 25 5 260 46 111 65 V7 8.4 Al ₂ (SO ₄ ) ₃ 0.15 1.5 20 2.7 29 2 3 50 164 114 V8 6.0 / H ₂ SO ₄ Al ₂ (SO ₄ ) ₃ 0.10 1.0 20 2.5 28 2 2 55 > 20 > 150 V9 8.4 KAl (SO ₄ ) ₂ 0.21 2.1 20 2.5 28 11 2 48 137 89 V10 6.0 / H ₂ SO ₄ KAl (SO ₄ ) ₂ 0.15 1.5 20 3.6 30 4 1 50 135 85

Is in column 2 of the above. Table given an acid (NCl, H ₂ SO ₄ ), this means that the specified pH was adjusted by addition of this acid.

In this example series, it is shown that when crumb laundry with deionized water is used only when CaCl _{2 is used} as the case electrolyte, nitrile rubbers with sufficient storage stability are obtained. The storage-stable nitrile rubbers have calcium amounts of 1235 to 1290 ppm.

Examples 11-20: (Inventive Examples and Comparative Examples) Storage stability of the nitrile rubber (28.9% by weight of acrylonitrile) obtained from latex A under the coagulation and washing conditions indicated in the following table.

The crumb wash was in all cases at 20 ° C and either with deionized water (DW) or calcium ion-containing water (BW) example Latex coagulation washing conditions ML1 + 4 @ 100 ° C [ME] pH of the latex type of salt Conc. Of saline solution
[Wt.%] Amount of salt bez. on NBR
[% By weight] T
[° C] Water type Time
[H] Chlorine content
[ppm] Ca
[ppm] mg
[ppm] MV1 MV2 LS 11 6.0 / H ₂ SO ₄ NaCl / DW 7 70 RT BW 7.75 110 805 25 48 48 0 12 6.0 / H ₂ SO ₄ NaCl / BW 7 70 RT BW 7.75 85 850 27 48 51 3 13 6.0 / HCl MgCl ₂ 0.8 8th RT BW 5.0 51 755 230 47 48 1 14 6.0 / HCl MgCl ₂ / CaCl ₂ 0.8 7.6 / 0.4 RT BW 5.0 52 890 170 51 46 -5 15 6.0 / HCl MgCl ₂ 0.8 8th RT BW 5 53 725 225 43 45 2 V16 6.0 / HCl MgCl ₂ 0.8 8th RT DW 5 36 10 225 40 59 19 17 6.0 / HCl MgCl ₂ 1.6 16 RT BW 5 88 750 265 44 46 2 V18 6.0 / HCl MgCl ₂ 1.6 16 RT DW 5.0 39 15 255 41 58 17 19 9.5 MgCl ₂ / CaCl ₂ 0.8 8 / 0.4 RT BW 5.0 49 490 106 45 48 3 20 9.5 MgCl ₂ / CaCl ₂ 0.8 8 / 0.4 RT BW 2.5 62 540 121 43 45 2

Is in column 2 of the above. Table indicates an acid (HCl, H ₂ SO ₄ ), this means that the specified pH was adjusted by adding this acid.

In the test series 2), it is shown that storage-stable nitrile rubbers are obtained by the use of non-deionized and thus water containing caustic (BW) in crumb washing. The use of deionized water (DW) in crumb washing does not lead to nitrile rubbers with sufficient storage stability. The storage-stable nitrile rubbers according to the invention contain Ca in quantities of 490 to 890 ppm.

Examples 21-31: (Inventive Examples) Storage stability of the nitrile rubber (28.9% by weight of acrylonitrile) obtained from latex A under the coagulation and washing conditions indicated in the following table.

The Krümelwäsche was carried out in all cases with calcium ion-containing water (BW). example Latex coagulation washing conditions ML1 + 4 @ 100 ° C [ME] pH of the latex type of salt Conc. Of saline solution
[Wt%] Amount of salt bez. on NBR
[Wt%] T
[° C] T
[° C] Time
[H] Chlorine content
[Ppm] Ca
[Ppm] mg
[Ppm] MV1 MV2 LS 21 8.4 NaCl 18 63 70 RT 2.5 240 610 21 47 47 3 22 8.4 NaCl 18 63 70 RT 10 170 560 24 48 47 3 23 8.4 NaCl 18 63 70 RT 5.0 220 705 19 46 49 3 24 8.4 NaCl 18 63 70 RT 15.0 230 645 18 48 48 3 25 8.4 NaCl 18 63 70 65 2.5 970 565 21 47 47 3 26 8.4 MgCl ₂ 35 2.71 RT RT 2.5 63 830 235 45 48 3 27 8.4 MgCl ₂ 35 2.71 45 60 5.0 44 610 107 45 48 3 28 8.4 MgCl ₂ 20 2.37 45 60 8th 86 400 83 46 47 3 29 8.4 MgCl ₂ 20 2.37 70 60 8th 97 215 101 46 46 3 30 8.4 MgCl ₂ 20 2.37 80 60 8th 120 225 107 46 48 3 31 8.4 MgCl ₂ 29 2.37 90 60 8th 76 171 111 46 48 3

In the example series 3) it is shown that storage-stable nitrile rubbers with Ca contents in the range of 171 ppm to 830 ppm are obtained by varying the conditions in latex coagulation and in crumb washing.

Examples 32-35: (Inventive Examples) Storage stability of the nitrile rubber (18.8% by weight of acrylonitrile) obtained from latex B under the coagulation and washing conditions indicated in the table below.

The Krümelwäsche was carried out in all cases with calcium ion-containing water (BW) example Latex coagulation washing conditions Chlorine content
[ppm] Ca
[ppm] ML 1 + 4 @ 100 ° C [ME] pH of the latex type of salt Conc. Of saline solution
[Wt.%] Amount of salt bez. on NBR
[Wt. %] T
[° C] T
[° C] Time
[H] MV1 MV2 LS 32 11.4 NaCl 26 64 90 60 8th 220 180 48 51 3 33 11.4 MgCl ₂ 35 1.8 90 60 8th 63 505 46 50 4 34 11.4 CaCl ₂ 10 1.63 90 60 8th 73 1225 47 44 -3 35 11.4 MgCl ₂ / Cal ₂ 35 1.08 / 0.12 90 60 8th 43 350 46 49 1

Example 36: (Inventive example) Storage stability of the nitrile rubber (38.6% by weight of acrylonitrile) obtained from latex C under the coagulation and washing conditions indicated in the table below.

Crumb washing was carried out with calcium ion-containing water (BW) example Latex coagulation washing conditions Chlorine content
[ppm] Ca
[ppm] ML 1 + 4 @ 100 ° C [ME] pH of the latex type of salt Conc. Of saline solution
[Wt.%] Amount of salt bez. On NBR
[Wt. %] T
[° C] T
[° C] Time
[H] MV1 MV2 LS 36 10.9 CaCl ₂ 0.3 1.8 90 60 8th 100 1930 47 51 4

Claims (24)

1. Nitrile rubber which contains repeating units of at least one α,β-unsaturated nitrile, at least one conjugated diene and optionally one or more further copolymerizable monomers and

   (i) has a calcium content of at least 150 ppm, based on the nitrile rubber, and a chlorine content of at least 40 ppm, based on the nitrile rubber, and

   (ii) contains 2,2,4,6,6-pentamethylheptane-4-thio and/or 2,4,4,6,6-pentamethylheptane-2-thio and/or 2,3,4,6,6-pentamethylheptane-2-thio and/or 2,3,4,6,6-pentamethylheptane-3-thio end groups.
2. Nitrile rubber according to Claim 1 which has a calcium content of at least 200 ppm, preferably at least 400 ppm, particularly preferably more than 500 ppm, in particular at least 600 ppm and especially preferably at least 800 ppm, of calcium, based on the nitrile rubber.
3. Nitrile rubber according to Claim 1 or 2 which has a storage stability SS of not more than 5 Mooney units, preferably less than 5 Mooney units and particularly preferably not more than 4 Mooney units, with the storage stability SS being given by the formula (I), $$\mathrm{SS}=\mathrm{MV}2-\mathrm{MV}1$$

   

   
   where

   MV1 is the Mooney viscosity of the nitrile rubber and

   MV2 is the Mooney viscosity of the same nitrile rubber after storage at 100°C for 48 hours.
4. Nitrile rubber according to one or more of Claims 1 to 3 containing repeating units of acrylonitrile, 1,3-butadiene and optionally one or more further copolymerizable monomers.
5. Nitrile rubber according to Claim 4 having repeating units of one or more α,β-unsaturated monocarboxylic or dicarboxylic acids, their esters or amides, preferably repeating units of an alkyl ester of an α,β-unsaturated carboxylic acid, in particular methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate or lauryl (meth)acrylate.
6. Nitrile rubber according to one or more of Claims 1 to 5 which has a Mooney viscosity MV1 (ML (1+4 @100°C)) of from 10 to 150 Mooney units, preferably from 20 to 100 Mooney units.
7. Nitrile rubber according to one or more of Claims 1 to 6 having a glass transition temperature in the range from -70°C to +10°C, preferably in the range from - 60°C to 0°C.
8. Nitrile rubber according to one or more of Claims 1 to 7 having 2,2,4,6,6-pentamethylheptane-4-thio, 2,4,4,6,6-pentamethylheptane-2-thio, 2,3,4,6,6-pentamethylheptane-2-thio and 2,3,4,6,6-pentamethylheptane-3-thio end groups.
9. Process for producing a nitrile rubber according to one or more of Claims 1-8 by emulsion polymerization of at least one α,β-unsaturated nitrile, at least one conjugated diene and optionally one or more further copolymerizable monomers, with the latex containing the nitrile rubber which is initially obtained in the polymerization being subjected to coagulation and the coagulated nitrile rubber obtained subsequently being washed, characterized in that

   (i) the emulsion polymerization is carried out in the presence of a mixture containing 2,2,4,6,6-pentamethylheptane-4-thiol, 2,4,4,6,6-pentamethylheptane-2-thiol, 2,3,4,6,6-pentamethylheptane-2-thiol and 2,3,4,6,6-pentamethylheptane-3-thiol,

   (ii) the latex containing the nitrile rubber which is obtained after the polymerization is subjected to coagulation using at least one salt selected from the group consisting of aluminium, calcium, magnesium, sodium, potassium and lithium salts,

   (iii) either a water-soluble calcium salt is present in the coagulation and/or the washing of the coagulated nitrile rubber is carried out using water containing calcium ions and

   (iv) a salt based on a chloride is present either during the emulsion polymerization, during the coagulation or during the subsequent washing of the coagulated nitrile rubber.
10. Process according to Claim 9, wherein the emulsion polymerization is carried out batchwise or continuously in a cascade of stirred vessels.
11. Process according to Claim 9 or 10, wherein one or more ageing inhibitors, preferably phenolic ageing inhibitors are added to the latex containing the nitrile rubber before or during coagulation.
12. Process according to one or more of Claims 9 to 11, wherein sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium nitrate, potassium nitrate, sodium sulphate, potassium sulphate, sodium hydrogencarbonate, potassium hydrogencarbonate, sodium carbonate, potassium carbonate, aluminium sulphate, potassium aluminium sulphate (potassium alum), sodium aluminium sulphate (sodium alum), sodium acetate, calcium acetate or calcium formate is used for the coagulation of the latex.
13. Process according to one or more of Claims 9 to 12, wherein the total amount of the salt or salts used for the coagulation of the latex is 0.5-200 parts by weight, preferably 0.8-80 parts by weight and particularly preferably 1-50 parts by weight, per 100 parts by weight of nitrile rubber.
14. Process according to one or more of Claims 9 to 13, wherein the latex used for the coagulation has a solids concentration in the range from 1% to 40%, preferably in the range from 5% to 35% and particularly preferably in the range from 15 to 30% by weight.
15. Process according to one or more of Claims 9 to 14, wherein the coagulation of the latex is carried out at a temperature in the range from 10 to 100°C, particularly preferably in the range from 20 to 90°C.
16. Process according to one or more of Claims 9 to 15, wherein the washing of the coagulated nitrile rubber is carried out at a temperature in the range from 15 to 90°C, preferably at a temperature in the range from 20 to 80°C.
17. Process according to one or more of Claims 9 to 16, wherein the nitrile rubber obtained is subsequently subjected (i) either only to a metathesis reaction or (ii) to a metathesis reaction and a subsequent hydrogenation or (iii) only to a hydrogenation.
18. Optionally hydrogenated nitrile rubbers obtainable by the process according to Claim 17.
19. Use of the nitrile rubbers according to one or more of Claims 1 to 8 or according to Claim 18 for producing vulcanizable mixtures.
20. Vulcanizable mixture containing at least one nitrile rubber according to one or more of Claims 1 to 8 or according to Claim 18, at least one crosslinker and optionally further additives.
21. Process for producing a vulcanizable mixture according to Claim 20 by mixing at least one nitrile rubber according to one or more of Claims 1 to 8 or according to Claim 18, at least one crosslinker and optionally further additives.
22. Process for producing mouldings based on a nitrile rubber according to one or more of Claims 1 to 8 or according to Claim 18, wherein a vulcanizable mixture according to Claim 20 is vulcanized in a shaping process, preferably using an injection moulding process.
23. Moulding obtainable by the process according to Claim 22.
24. Moulding according to Claim 23, characterized in that it is a seal, a cap, a hose or a diaphragm, in particular an O-ring seal, a flat seal, a corrugated sealing ring, a sealing sleeve, a sealing cap, a dust protection cap, a plug seal, a thermal insulation hose (with or without addition of PVC), an oil cooler hose, an air intake hose, a servo control hose or a pump diaphragm.